Thoughts on: The Selection of Design, Gorgon L. Glegg

The Selection of Design is short – really short, it maybe takes an hour to read through. This is understandable, looking at the timeline of books written by Glegg this is the second, written four years after The Design of Design, which I enjoyed greatly. Unfortunately it suffers the fate of many second outputs, it fails to live up to the first as it only contains a few years of wisdom, whereas the first contained the best ideas of most of a career.

Many of the ideas are interesting and some are thought provoking, though there are some that do not feel are fully thought through.

  • There is little simple engineering left – or at least there shouldn’t be… disagree with this – changes in opportunity and materials allow simple solutions where previously a workaround was required
  • Try to focus your thought when starting to solve a problem at the ‘interfaces’ to make these, often hard to analyse, parts simple – in the case of a manufacturing run this is often at the interface where, up to the interface, value is measured in weight (to help account for variation in density) and afterwards it is measured in volume. For other systems the interfaces can often be seen at points where the types of energy change radically. There is usually more than one interface in each system. When designing, start from each of these interfaces and work outwards. Agree with this.
  • As a strategy when faced with difficult and highly constrained problems, try solving the problem several times, each time with one of the constraints removed – what is common between these solutions? Try to reimpose the final condition by adjusting one of the partial designs. Agree with this.
  • Think about the context of the thing you are designing in its entirety and think about ways it might vary from your common experience – an example given is moisture in the air condensing on cool objects, making them wet, another that vibrations make nuts fall off bolts, changing the conditions of the machine.
  • When choosing between designs of seemingly equal merit, give benefit to the one that is statically determinate (or easy to analyse accurately), this reduces the risk by allowing a more informed design. If both are determinate and easy enough to analyse accurately, choose the one that is “complicated*” and “could not have been done 5 years ago”. I disagree with the latter – the assumption that all neat design solutions have already been found is certainly not true in structural engineering.
    • * Complicated is justified later – something with unneeded complications is bad, something with appropriate complexity tends to be good. Glegg is still advocating the approach of ‘divide and tidy up’ from The Design of Design, but is now pushing towards a paradigm of a fairly direct mapping of function to components, this is advocated over a many functions to few components approach largely to increase the effectiveness of any one component – I agree with this. However, in the context of another constraint the combining of functions might well be well worthwhile despite impacts on individual component’s efficiency, for example, reducing the weight of a racing car by using the block of the engine as part of the structure of the car.
  • Differentiating between possible impossibilities and intrinsic impossibilities – use basic principles, not only from physics and engineering, but also from accounting, psychology etc.
  • When faced with an impossibility do not try to negotiate a compromise – the right solution will not lie there, instead, try to make some of the impossibility dissolve through a clever solution, or one that moves a part of the impossibility elsewhere where it can be easily managed.
  • Value simplicity only for its more direct virtues, such as reliability and cheapness. There is no intrinsic value in simplicity itself. Furthermore, an oversimplified design can be vulnerable to small variations between the model and the real world which a more complicated design is able to accommodate.
  • Work with the material and its effects wherever you can – use expansion to create beneficial internal stresses, change the material (e.g. heating or cooling it) so it works for you rather than fighting it

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Now with complementary bookmark – good choice Keith Blacks. Who knew the Spice Girls were still touring together in 2008?

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